org.h2.command.dml

Class Select

java.lang.Object

org.h2.command.Prepared

org.h2.command.dml.Query

org.h2.command.dml.Select

public class Select
extends Query

This class represents a simple SELECT statement. For each select statement, visibleColumnCount <= distinctColumnCount <= expressionCount. The expression list count could include ORDER BY and GROUP BY expressions that are not in the select list. The call sequence is init(), mapColumns() if it's a subquery, prepare().

Author:

Thomas Mueller, Joel Turkel (Group sorted query)

Field Summary

Fields inherited from class org.h2.command.dml.Query

distinct, limitExpr, offsetExpr, randomAccessResult, sampleSize

Fields inherited from class org.h2.command.Prepared

create, parameters, prepareAlways, session, sqlStatement

Constructor Summary

Constructors

Constructor and Description
Select(Session session)

Method Summary

Methods

Modifier and Type	Method and Description
void	addCondition(Expression cond) Add a condition to the list of conditions.
void	addGlobalCondition(Parameter param, int columnId, int comparisonType) Add a condition to the query.
void	addTableFilter(TableFilter filter, boolean isTop) Add a table to the query.
void	fireBeforeSelectTriggers() Call the before triggers on all tables.
int	getColumnCount() Get the column count of this query.
double	getCost() Calculate the cost to execute this query.
HashMap<Expression,Object>	getCurrentGroup()
int	getCurrentGroupRowId()
ArrayList<Expression>	getExpressions() The the list of select expressions.
String	getPlanSQL() Get the SQL statement with the execution plan.
HashSet<Table>	getTables() Get all tables that are involved in this query.
ArrayList<TableFilter>	getTopFilters()
TableFilter	getTopTableFilter()
int	getType() Get the command type as defined in CommandInterface
void	init() Initialize the query.
boolean	isCacheable()
boolean	isEverything(ExpressionVisitor visitor) Check if this expression and all sub-expressions can fulfill a criteria.
boolean	isQuickAggregateQuery() Check if this is an aggregate query with direct lookup, for example a query of the type SELECT COUNT(*) FROM TEST or SELECT MAX(ID) FROM TEST.
boolean	isReadOnly() Check if this command is read only.
void	mapColumns(ColumnResolver resolver, int level) Map the columns to the given column resolver.
void	prepare() Prepare this statement.
ResultInterface	queryMeta() Get an empty result set containing the meta data.
protected LocalResult	queryWithoutCache(int maxRows, ResultTarget target) Execute the query without checking the cache.
void	setEvaluatable(TableFilter tableFilter, boolean b) Change the evaluatable flag.
void	setExpressions(ArrayList<Expression> expressions)
void	setForUpdate(boolean b) Set the 'for update' flag.
void	setGroupBy(ArrayList<Expression> group)
void	setGroupQuery() Called if this query contains aggregate functions.
void	setHaving(Expression having)
void	setOrder(ArrayList<SelectOrderBy> order) Set the order by list.
void	updateAggregate(Session s) Update all aggregate function values.

Methods inherited from class org.h2.command.dml.Query

disableCache, getCostAsExpression, getMaxDataModificationId, getParameterValues, isQuery, isTransactional, prepareOrder, query, setDistinct, setLimit, setOffset, setRandomAccessResult, setSampleSize

Methods inherited from class org.h2.command.Prepared

checkCanceled, checkParameters, getCurrentObjectId, getCurrentRowNumber, getObjectId, getParameters, getSQL, getSQL, getSQL, needRecompile, setCommand, setCurrentRowNumber, setObjectId, setParameterList, setPrepareAlways, setRow, setSession, setSQL, toString, update

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Select

public Select(Session session)

Method Detail

addTableFilter

public void addTableFilter(TableFilter filter,
                  boolean isTop)

Add a table to the query.

Parameters:

filter - the table to add

isTop - if the table can be the first table in the query plan

getTopFilters

public ArrayList<TableFilter> getTopFilters()

setExpressions

public void setExpressions(ArrayList<Expression> expressions)

setGroupQuery

public void setGroupQuery()

Called if this query contains aggregate functions.

setGroupBy

public void setGroupBy(ArrayList<Expression> group)

getCurrentGroup

public HashMap<Expression,Object> getCurrentGroup()

getCurrentGroupRowId

public int getCurrentGroupRowId()

setOrder

public void setOrder(ArrayList<SelectOrderBy> order)

Description copied from class: Query

Set the order by list.

Specified by:

setOrder in class Query

Parameters:

order - the order by list

addCondition

public void addCondition(Expression cond)

Add a condition to the list of conditions.

Parameters:

cond - the condition to add

queryMeta

public ResultInterface queryMeta()

Description copied from class: Prepared

Get an empty result set containing the meta data.

Specified by:

queryMeta in class Prepared

Returns:

the result set

queryWithoutCache

protected LocalResult queryWithoutCache(int maxRows,
                            ResultTarget target)

Description copied from class: Query

Execute the query without checking the cache. If a target is specified, the results are written to it, and the method returns null. If no target is specified, a new LocalResult is created and returned.

Specified by:

queryWithoutCache in class Query

Parameters:

maxRows - the limit as specified in the JDBC method call

target - the target to write results to

Returns:

the result

init

public void init()

Description copied from class: Query

Initialize the query.

Specified by:

init in class Query

prepare

public void prepare()

Description copied from class: Prepared

Prepare this statement.

Overrides:

prepare in class Prepared

getCost

public double getCost()

Description copied from class: Query

Calculate the cost to execute this query.

Specified by:

getCost in class Query

Returns:

the cost

getTables

public HashSet<Table> getTables()

Description copied from class: Query

Get all tables that are involved in this query.

Specified by:

getTables in class Query

Returns:

the set of tables

fireBeforeSelectTriggers

public void fireBeforeSelectTriggers()

Description copied from class: Query

Call the before triggers on all tables.

Specified by:

fireBeforeSelectTriggers in class Query

getPlanSQL

public String getPlanSQL()

Description copied from class: Prepared

Get the SQL statement with the execution plan.

Overrides:

getPlanSQL in class Prepared

Returns:

the execution plan

setHaving

public void setHaving(Expression having)

getColumnCount

public int getColumnCount()

Description copied from class: Query

Get the column count of this query.

Specified by:

getColumnCount in class Query

Returns:

the column count

getTopTableFilter

public TableFilter getTopTableFilter()

getExpressions

public ArrayList<Expression> getExpressions()

Description copied from class: Query

The the list of select expressions. This may include invisible expressions such as order by expressions.

Specified by:

getExpressions in class Query

Returns:

the list of expressions

setForUpdate

public void setForUpdate(boolean b)

Description copied from class: Query

Set the 'for update' flag.

Specified by:

setForUpdate in class Query

Parameters:

b - the new setting

mapColumns

public void mapColumns(ColumnResolver resolver,
              int level)

Description copied from class: Query

Map the columns to the given column resolver.

Specified by:

mapColumns in class Query

Parameters:

resolver - the resolver

level - the subquery level (0 is the top level query, 1 is the first subquery level)

setEvaluatable

public void setEvaluatable(TableFilter tableFilter,
                  boolean b)

Description copied from class: Query

Change the evaluatable flag. This is used when building the execution plan.

Specified by:

setEvaluatable in class Query

Parameters:

tableFilter - the table filter

b - the new value

isQuickAggregateQuery

public boolean isQuickAggregateQuery()

Check if this is an aggregate query with direct lookup, for example a query of the type SELECT COUNT(*) FROM TEST or SELECT MAX(ID) FROM TEST.

Returns:

true if a direct lookup is possible

addGlobalCondition

public void addGlobalCondition(Parameter param,
                      int columnId,
                      int comparisonType)

Description copied from class: Query

Add a condition to the query. This is used for views.

Specified by:

addGlobalCondition in class Query

Parameters:

param - the parameter

columnId - the column index (0 meaning the first column)

comparisonType - the comparison type

updateAggregate

public void updateAggregate(Session s)

Description copied from class: Query

Update all aggregate function values.

Specified by:

updateAggregate in class Query

Parameters:

s - the session

isEverything

public boolean isEverything(ExpressionVisitor visitor)

Description copied from class: Query

Check if this expression and all sub-expressions can fulfill a criteria. If any part returns false, the result is false.

Specified by:

isEverything in class Query

Parameters:

visitor - the visitor

Returns:

if the criteria can be fulfilled

isReadOnly

public boolean isReadOnly()

Description copied from class: Prepared

Check if this command is read only.

Overrides:

isReadOnly in class Prepared

Returns:

true if it is

isCacheable

public boolean isCacheable()

Overrides:

isCacheable in class Prepared

getType

public int getType()

Description copied from class: Prepared

Get the command type as defined in CommandInterface

Specified by:

getType in class Prepared

Returns:

the statement type